Glaucoma is a group of ocular disorders characterized by progressive loss of retinal ganglion cells and their axons, and a gradual loss of visual field. It is one of the leading causes of blindness worldwide. Glaucoma has a prevalence of about 1-2% in the general population in Europe. Up to 3-4% of people aged over 60 are affected by the disease. The most common form of glaucoma is the primary open-angle glaucoma (POAG), with a prevalence ranging from 1.1% to 2%.
The pathogenesis of glaucoma is only partly understood and an elevated intraocular pressure is not solely responsible for the disease. An increased intraocular pressure is still considered as a major risk factor, but other pathogenic factors, such as apoptotic processes, elevated nitric oxide levels or an involvement of the immune system are likely to be relevant.
Furthermore, an elevated intraocular pressure is quite prevalent (10% of the population at age 40), however, only some of these develop glaucoma over the years. So far there are no standard diagnostic tests to identify which persons with an elevated intraocular pressure develop glaucoma. Since an early treatment of glaucoma is crucial to prevent loss of vision, there is a need for improved diagnostic tools, which detect glaucoma at an early stage independent of an elevated intraocular pressure.
An elevated intraocular pressure is known as a major cause for retinal cell death and the development of the glaucoma disease. Elevated pressure as a cause for cell death has been reproduced in vitro. Agar et al. (Brain Res. 2006. 1086 (1): p. 191-200) exposed in vitro cultures of retinal ganglion cell lines to elevated hydrostatic pressure and induced cell death.
However, it is also known that about 30% of the glaucoma cases are not accompanied by an elevated intraocular pressure. At least some forms of the Glaucoma disease fit the pattern of neurodegenerative diseases with progressive dysfunction of aspects of the nervous system along with progressive atrophy of the affected structures of the peripheral or central nervous system. Therefore, further causes and mechanisms are discussed, which besides an elevated intraocular pressure are leading to the destruction of retinal ganglion cells such as for example an elevated nitric oxide level or a T-cell mediated process or autoimmune attacks.
Early detection methods for Glaucoma are still limited. Measuring the intraocular pressure can detect some of the patients but fluctuant pressure levels can also give a false negative result. At the time, when patients themselves recognize a loss of visual function, a large irreversible defect of retinal ganglion cells has in most cases already occurred.
The roughly 30% of the glaucoma cases which are not accompanied by an elevated intraocular pressure are termed as normal tension glaucoma. The traditional detection method measuring an elevated intraocular pressure fails with these patients. Considering the lack of a diagnostic method for normal tension glaucoma as well as the lack of a detection method for early stage glaucoma, it is necessary to develop methods for detecting glaucoma independent of the intraocular pressure. Autoimmunity as an important factor in Glaucoma has been demonstrated by several studies showing serum antibodies against ocular antigens. For example, heat shock proteins HSP27, HSP60, α-B-crystallin, γ-enolase, α-fodrin, gluthathione-S-transferase, and glycosaminoglycans, have different levels of binding reactivities in glaucoma patients compared to healthy subjects (e.g. Joachim, S. C., et al., Curr. Eye Res. 2007, 32 (6): p. 501-9.) Interestingly, not only elevated antibody reactivities, which might have an autoagressive impact, but for certain antigens diminished autoimmune reactivities are characteristic in bodyfluids of glaucoma patients. Furthermore, it could be shown that the direct application of anti-HSP antibodies results in an apoptosis of retinal ganglion cells in a cell culture approach (Tezel G, et al. Invest Ophthalmol. Vis. Sci. 1998; 39:2277-2287).
Previously, diagnostic methods based on the specific autoimmune reactivity pattern of glaucoma patients were disclosed. For example, WO2004/036220 discloses methods for diagnosis of glaucoma by the analysis of the complex autoantibody repertoire in body fluids such as serum, tears, aqueous humor or saliva against ocular antigens. As source for ocular antigens crude mixtures of retinal antigens, optic nerve antigens and others have been used and the complex autoimmune reactivity patterns have been measured. A variety of analytical immunological techniques including Western blot assays, chemiluminescence assay, ELISA, Radioimmunoassays for detection and measurement of the autoimmune reactivity patterns as well as methods for digital image detection, processing and analysis were used for the generation and comparative analysis of the autoimmune reactivity patterns of test individuals, healthy individuals and glaucoma patients were disclosed. The WO2004/036220 document teaches diagnostic methods for glaucoma relying on the autoimmune reactivity patterns against ocular antigens, which are not isolated from complex mixtures of a large number of ocular antigens and most of which have not been identified. The difference of the autoimmune reactivity patterns in body fluids from test individuals, healthy individuals and glaucoma patients then yields the diagnostic result. However, studies in the diagnostic field concerning other diseases such as cancer have revealed, that diagnosis based on autoimmune reactivity against biomarkers of unknown identity is often unreliable. Thus there is a need for reliable methods of diagnosis of glaucoma, which are independent of an elevated intraocular pressure.
It is an object of the current invention to provide alternate and improved and reliable diagnostic methods to detect glaucoma independent of an increased intraocular pressure by analysis of body fluids. It is a further object of the invention to provide diagnostic methods to detect glaucoma with selectable degrees of sensitivity and specificity used for both for rapid testing and for professional laboratory testing. Further objects of the invention include the provision of antigen carrying elements and kits for diagnosing glaucoma as well as newly identified ocular antigens serving as biomarkers for diagnosing glaucoma and as blocking agents in the therapeutic treatment of glaucoma.